Apparatus for polishing a wafer

ABSTRACT

A chemical mechanical polishing (CMP) apparatus includes a polishing pad, a platen, and a cleaning apparatus which provides a cleaning fluid for cleaning the polishing head. The cleaning apparatus includes a shaft located outside a periphery of the polishing pad, and an arm mounted to the shaft and extending over the polishing pad such that a bottom surface of the arm confronts the polishing surface of the polishing pad. Further, a cleaning fluid path is defined in the arm along a length of the arm, and first drop holes are defined in the arm which are fluidly connected to the cleaning fluid path and which drop cleaning fluid onto the polishing surface of the polishing pad.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to chemical mechanical polishing (CMP) and, more particularly, the present invention relates to a CMP apparatus for polishing a film formed on a wafer surface.

[0003] 2. Description of the Related Art

[0004] Chemical mechanical polishing (CMP) is one accepted method of planarization. In a typical CMP apparatus, the exposed surface of a substrate is placed against a polishing pad that is mounted upon a circular rotatable plate (so-called “platen”). A polishing head tightly holds the substrate, and a pressure is applied bring the surface of the substrate against the polishing pad. Slurry is supplied onto the polishing pad to remove or abrade the surface of the substrate. A reagent in the slurry reacts on a film formed on the substrate surface to facilitate the polishing. Reactions of the substrate surface, the reagent, the polishing pad, and frictional particles make it possible to polish the film.

[0005] One problem encountered in connection the CMP apparatus is that the polishing pad can easily become contaminated by materials removed from the slurry and the substrate. Further, the removed materials can deteriorate the effectiveness of subsequent polishing processes. Accordingly, it is a general practice to clean the pad during and/or between polishing processes.

[0006] One apparatus for cleaning a polishing pad using a rinse arm is disclosed in U.S. Pat. No. 6,280,299 entitled “COMBINED SLURRY DISPENSER AND RINSE ARM” issued to the Applied Materials Inc., issued on Feb. 16, 2000. In this apparatus, high-pressure de-ionized (DI) water for cleaning a polishing pad is sprayed at high pressure through spray nozzles. However, apparatus of this type suffer a number of drawbacks. For example, the high pressure of the sprayed DI water cause the slurry to rebound (or splash) so as to be dispersed all over the polishing apparatus, resulting in slurries which solidify at the rinse arm and the polishing head, referred to here as a second contamination. Particularly, most slurries rebounding off the polishing pad stick to a guard inner wall of a guard of the rinse arm. The slurries solidified on the guard inner wall tend to drop down onto the polishing pad in the polishing process to cause macro and micro snatches, which reduces yields. These slurries solidified on the guard inner wall are the principal factor in the generation of particles and scratches. Further, the high-pressure DI water, which is sprayed through spray nozzles, results in a fume phenomenon where an inside of the polishing apparatus is contaminated on an air current. Also, since the machine operator cannot readily access slurries sticking to the guard inner wall of the rinse arm, the rinse arm must be detached from the polishing apparatus in order to clean the rinse arm (or remove the slurries). Likewise, since the rinse arm is opened to an end without a guard, any DI water splashed thereto can contaminate a rotating polishing head that holds the wafer in front of a rinse arm. Finally, eddy currents may be formed in the rinse arm by the spray angle of spray nozzles when the high-pressure DI water is supplied. These eddy current in the rinse arm can disadvantageously result in a partial oversupply phenomenon.

[0007] Generally, when high-pressure DI water is sprayed so as to clean a polishing pad after supplying slurries to the polishing pad, slurries and contaminants on the polishing pad are splashed so as to adhere to the rinse arm (particularly, the guard inner wall) and peripheral devices. For example, slurries or contaminants at a bottom of the polishing pad can mixed with the splashed high-pressure DI water. If the slurries or contaminants adhere to each internal part of the polishing apparatus, they can dry (solidify) to become a source of particle contamination and a micro-scratches. Micro-scratches are particularly damaging to yields as they often result in the electrical shorting of insulating layers, a gate brigdes and so forth. Moreover, if the slurries and contaminants remain at internal edges of the polishing apparatus, it is nearly impossible to effectively perform the cleaning process, thus reducing the overall reliability of the CMP process.

SUMMARY OF THE INVENTION

[0008] According to an embodiment of the present invention, an apparatus for planarizing wafers includes a polishing pad, a platen, and a cleaning apparatus which provides a cleaning fluid for cleaning the polishing head. The cleaning apparatus includes a shaft located outside a periphery of the polishing pad, and an arm mounted to the shaft and extending over the polishing pad such that a bottom surface of the arm confronts the polishing surface of the polishing pad. Further, a cleaning fluid path is defined in the arm along a length of the arm, and first drop holes are defined in the arm which are fluidly connected to the cleaning fluid path and which drop cleaning fluid onto the polishing surface of the polishing pad.

[0009] The arm of the cleaning apparatus may further include a second drop hole which is fluidly connected to the cleaning fluid path and which drops the cleaning fluid onto a side surface of the polishing head. The second drop hole may be located at a distal end of the arm adjacent to the side surface of the polishing head.

[0010] At least one slurry path may further be defined in the arm along the length of the arm, and the apparatus further include a nozzle fluidly connected to the slurry path to supply slurry onto the polishing pad. A the nozzle may be inserted into a receiving hole which is defined in the arm and which has a hole, communicating with the slurry path, into which the nozzle is inserted.

[0011] The arm of the cleaning apparatus may be formed of a monolithic body, and may have a first portion which extends lengthwise from the base, a second portion which extends lengthwise at an angle from the first portion, and a third portion which extends lengthwise at an angle from the second portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other aspects and features of the present invention will become readily understood from the detailed description that follows, with reference to the accompanying drawings, in which:

[0013]FIG. 1 is an exploded view of a CMP apparatus according to an embodiment of the present invention;

[0014]FIG. 2 is a partial top plan view of the CMP apparatus shown in FIG. 1;

[0015]FIG. 3 is a cross-sectional view of a cleaning arm taken along a line I-I′ of FIG. 2;

[0016]FIG. 4 is a partial cross-sectional view of the cleaning arm shown in FIG. 2; and

[0017]FIG. 5 is a partial cross-sectional side view of the CMP apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Referring initially to FIG. 1, a CMP apparatus 100 according to an embodiment of the present invention will be described. As shown, the CMP apparatus 100 generally includes a polishing station 110, a polishing head assembly 150, and a cleaning apparatus 130.

[0019] The polishing head assembly 150 has a polishing head 152, a drive shaft 154, and a motor 156. A wafer (not shown) is mounted to the polishing head 152, and the polishing head 152 provides a controllable pressure so as to push the wafer against the polishing pad 122. The polishing head 152 may be rotated by means of the drive shaft 154 at 40-70 rpm. Of course, the rate of rotation may be higher or lower than 40-70 rpm. Although not shown, two or more negative air pressure or vacuum channels may be contained in the polishing head 152 to suction mount the wafer. Of course, respective pumps would then be connected to such channels.

[0020] The polishing station 110 has a rotatable platen 120 to which the polishing pad 122 is attached. The platen 120 is coupled to a platen rotating device such as a motor and rotatable shaft (not shown). Under an ideal state, the platen rotating device rotates the platen 120 at 50-80 rpm. Of course, the rate of rotation may be higher or lower than 50-80 rpm. The polishing pad 122 may be a combination material having a rough polishing surface. The polishing station 110 may also include a conditioning device 114 as is know in the art.

[0021] The cleaning apparatus 130 serves to clean the polishing pad 122 and a side of the polishing head 152 which are contaminated by slurry during a planarization process, and further serves to provide the slurry used in the planarization process. The cleaning apparatus 130 removes solidified slurry and contaminants on a surface of the polishing pad 122 and in grooves thereof. For example, the slurry may include a reagent (e.g., DI water for oxidation polishing), frictional particles (e.g., silicon dioxide for oxidation polishing), and a chemical reaction catalyst (e.g., calcium hydroxide for oxidation polishing).

[0022] The cleaning apparatus 130 will now be described more fully with reference to FIG. 2 through FIG. 5, in which like elements are identified by the same reference numbers. Particularly, FIG. 2 is a partial top plan view of the CMP apparatus shown in FIG. 1, FIG. 3 is a cross-sectional view of the cleaning arm 134 taken along a line I-I′ of FIG. 2, FIG. 4 is a partial cross-sectional view of the cleaning arm shown in FIG. 2, and FIG. 5 is a partial cross-sectional side view of the CMP apparatus shown in FIG. 1.

[0023] The cleaning apparatus 130 includes a shaft 132 that is disposed outside the periphery of platen 120, and an arm 134 that is pivotably coupled to the shaft 132 and disposed so as to extend over the polishing pad 122.

[0024] The arm 134 is pivotably mounted upon the shaft 132 in order to be rotated between a cleaning position over the polishing pad 122 and a stand-by position adjacent to the platen 120. The arm 134, which is preferably formed of a monolithic (one piece) body, has a base portion 134 a coupled to the shaft 132, a first extension 134 b extending from the base 134 a, a second extension 134 c extending at an angle relative to and from the first extension 134 b, and a third extension 134 d extending at an angle relative to and from the second extension 134 c. The extensions 134 b, 134 c, and 134 d that are formed in an angled relation to allow the end 134 e of the arm 134 to be placed closely adjacent to the polishing pad 152 while avoiding a collision between the remainder of the arm 134 and the polishing pad 152.

[0025] As shown in FIG. 5, a barrier wall 135 may be formed at a bottom of the base 134 a. The barrier wall 135 prevents slurry and unwanted debris from splashing into the shaft during a planarization or cleaning process.

[0026] Referring to FIG. 3 and FIG. 4, the arm 134 has a cleaning water transfer path 136 and a slurry transfer path 140. A cleaning water is transferred to first drop holes 137 and second drop holes 138 through the cleaning water transfer path 136. Slurry is transferred to a nozzle 142, which is installed at the third extension 134 d of the arm 134, through the slurry transfer path 140. The first drop holes 137 are spaced apart at a bottom of the arm 134 along a length of the arm 134. At least one of the first drop hole 137 may disposed to drop the cleaning water onto a sidewall of the platen 120 (see FIG. 5). The second drop holes 138 are formed at an end side of the arm 134 (i.e., the third extension 134 d). For example, the second drop holes 138 are preferably formed at a position nearest the side of the polishing head 152. Referring to FIG. 5, the cleaning water expelled from the first drop holes 137 cleans the polishing pad 122 and a side 120 a of the platen 120. The cleaning water expelled from the second drop hole 138 cleans a side of the polishing head 152.

[0027] The arm 134 may have a flat bottom surface, but, referring to FIG. 3, the arm 134 preferably has an arch-shaped bottom surface 139 to minimize surface area which horizontally confronts the polishing pad 122, thus reducing the amount of unwanted debris (including slurry) that will stick to the bottom of the arm 134. Advantageously, the arch-shaped bottom surface 139 also enhances access to the bottom of the arm 134, thus facilitating cleaning of the arm by the machine operator. Of course, the bottom surface of the arm 134 may be formed in other ways, such as by inclined walls and so on.

[0028] Referring to FIG. 5, cleaning water drops onto a surface of the polishing pad 122 through the first drop holes 137 to clean the surface of the polishing pad 122 and a side 120 a of the platen 120. Cleaning water is also dropped from the second drop holes 138 along a side of the polishing head 152 to prevent unwanted debris including slurry from being solidified on the side of the polishing head 152.

[0029] As shown above, the cleaning water flows through and drops from the drop holes of the arm 134. Since the water is not expelled under high-pressure by a nozzle, splashing is avoided or minimized. Likewise, the fume phenomenon can be avoided as well.

[0030] Returning to FIG. 2, the cleaning apparatus 130 has a slurry transfer path 140 that is formed in the arm 134, and a nozzle 142 that is connected to the slurry transfer path 140 and sprays slurry onto the polishing pad. The nozzle 142 is for spraying slurry onto the polishing pad 122 during polishing and is inserted or screwed into a hole 144. The hole 144 is formed at the third extension of the arm 134 and is connected to the slurry transfer path 140.

[0031] Although not shown in the figure, paths for sending fluid to the arm 134 are formed at the shaft 132. Theses paths supply needed fluid from supply sources associated with the CMP apparatus to the cleaning water transfer path and the slurry transfer path of the arm 134.

[0032] The present invention is thus not limited to the details of the illustrated embodiment. Accordingly, the above description and drawings are only to be considered illustrative of exemplary embodiments which achieve the features and advantages of the present invention. Modifications and substitutions to specific process conditions and structures may be made without departing from the spirit and scope of the present invention. Therefore, the invention is not to be considered as being limited by the foregoing description and drawings, but is only limited by the scope of the appended claims. 

What is claimed is:
 1. An apparatus for planarizing wafers, comprising: a polishing station having a platen to which a polishing pad having a polishing surface is attached; a polishing head located over the polishing surface of the polishing pad; and a cleaning apparatus which supplies a cleaning fluid onto the polishing pad, and which includes a shaft located outside a periphery of the polishing pad, and an arm mounted to the shaft and extending over the polishing pad such that a bottom surface of the arm confronts the polishing surface of the polishing pad; wherein a cleaning fluid path is defined in the arm along a length of the arm, and wherein first drop holes are defined in the arm which are fluidly connected to the cleaning fluid path and which drop cleaning fluid onto the polishing surface of the polishing pad.
 2. The apparatus as recited in claim 1, wherein the bottom surface of the arm is a flat surface.
 3. The apparatus as recited in claim 1, wherein the bottom surface of the arm is a curved surface.
 4. The apparatus as recited in claim 2, wherein the first drop holes are formed at the bottom surface of the arm.
 5. The apparatus as recited in claim 3, wherein the first drop holes are formed at the bottom surface of the arm.
 6. The apparatus as recited in claim 1, wherein the arm further includes at least one second drop hole which is fluidly connected to the cleaning fluid path and which drops the cleaning fluid onto a side surface of the polishing head.
 7. The apparatus as recited in claim 6, wherein the second drop hole is located at a distal end of the arm adjacent to the side surface of the polishing head.
 8. The apparatus as recited in claim 1, wherein at least one slurry path is further defined in the arm along the length of the arm, and wherein the apparatus further includes a nozzle fluidly connected to the slurry path to supply slurry onto the polishing pad.
 9. The apparatus as recited in claim 8, wherein the nozzle is inserted into a receiving hole which is defined in the arm and which has a hole, communicating with the slurry path, into which the nozzle is inserted.
 10. The apparatus as recited in claim 1, wherein the arm has a first portion which extends lengthwise from the base, a second portion which extends lengthwise at an angle from the first portion, and a third portion which extends lengthwise at an angle from the second portion.
 11. The apparatus as recited in claim 10, wherein the arm is formed of a monolithic body.
 12. The apparatus as recited in claim 1, wherein the cleaning water is a de-ionized (DI) water. 